1. Technical Field
The present disclosure generally relates to ultrasound imaging systems and methods. Particularly, the present disclosure relates to speckle reduction in ultrasound images.
2. Description of Related Art
Today, many surgical procedures are performed through small openings in the skin, as compared to the larger openings typically required in traditional procedures, in an effort to reduce both trauma to the patient and recovery time. Such procedures are known as “minimally invasive” procedures. During the course of minimally invasive procedures, the nature of the relatively small opening through which surgical instruments are manipulated, and/or the presence of sub-surface tissue structures, may obscure a direct line-of-sight to the target surgical site. Accordingly, it would be desirable to provide a method of sub-surface visualization that is not limited by the geometry of the minimally invasive surgical site.
One such technique involves the use of ultrasound to provide clinicians with the ability to image sub-surface tissue structures. Ultrasound imaging relies on different acoustic impedances of adjacent tissue structures to provide the contrast used for imaging and identifying separate tissue structures. Ultrasound imaging possesses several advantages that are attractive for real-time application in surgical procedures, e.g., minimal associated radiation and relatively small and inexpensive imaging hardware.
One type of ultrasound imaging technique is a B-mode, which obtains a two-dimensional cross-section of the tissue being imaged. The B-mode ultrasound technique always generates random speckle noise in the image. Speckle is a random, deterministic interference pattern in an image formed with coherent radiation of a medium containing many sub-resolution scatters. The texture of the observable speckle pattern does not correspond to underlying structures. To reduce the noise, a technique called compound imaging steers acoustic energy at different angles and averages the values of the pixels at each location obtained using acoustic signals from different angles.
Due to limitations in a traditional linear array, the acoustic energy is generally steered less than 20°. Because there is a lot of overlap even after the beams are steered, there is a strong correlation between signals from steered beams. The speckle pattern generated by these beams is therefore highly correlated thereby limiting the effect of the compounding technique.